Hypodermic fluid dispensers fall into two broad categories, namely: needle hypodermic dispensers and jet injectors. Jet injectors are particularly useful in immunization programs which involve the delivery of a non-living virus; and needle injectors are useful in the delivery of a non-living virus and of medications.
In general, jet inoculation, as compared to needle inoculation, is less traumatic, presents a lower risk of cross contamination, requires less operator training, and allows a higher number of procedures per unit of time.
Although both needle hypodermic injectors and high pressure jet injectors have been widely used, the presently known devices have serious disadvantages. The problems associated with needle injectors in the spread of AIDS (Acquired Immune Deficiency Syndrome ) alone is sufficient motivation to avoid proliferation of today's needle systems. People cannot be relied upon to dispose of needle injectors in accordance with instructions and good practice; and an element of the population are tempted to reuse needles without knowledge of or regard for safe practices.
Jet injectors generally avoid the above referenced problems associated with needle injectors; however, the presently available injectors are expensive; prone to failure; too bulky to transport conveniently; and are generally inconvenient to use.